1. Field of the Invention
The present invention relates to a magneto-resistance effect element for reading an information signal recorded on a magnetic recording medium as well as to a magneto-resistance effect sensor, a magneto-resistance effect detection system, and a magnetic storage system using the magneto-resistance effect element.
2. Description of the Related Art
Conventionally, a magnetic reading converter is known with a name of an MR sensor or an MR head. It is known that data can be read from a magnetic surface with a large linear density. The MR sensor detects a magnetic field signal via a resistance change as a function of an intensity and a direction of the magnetic flux sensed by a reading element. Such an MR sensor of a conventional technique operates according to an anistoropic magneto-resistance (AMR) effect in which a resistance component of a reading element changes in proportion to the square of a cosine of an angle between a magnetization direction and a sensing current flowing in the element. A more detailed explanation on the AMR effect is given in D. A. Thomson et al, "Memory, Storage and Related Applications" IEEE Trans. On Mag. MAG-11, p. 1039 (1975). In a magnetic head using the AMR effect, a longitudinal bias is usually applied so as to suppress the Barkhausen noise. This longitudinal bias is applied, for example, by using an antiferromagnetic material such as FeMn, NiMn, and a nickel oxide.
Furthermore, recent publications describe a more remarkable magneto-resistance effect in which a resistance change of a layered magnetic sensor attributes to a conductive electron spin-dependant transmission between magnetic layers via a non-magnetic layer accompanied by a spin-dependant scattering on the layer boundary surface. This magneto-resistance effect is called with various names such as "giant magneto-resistance effect" and "spin bulb effect". Such an MR sensor is made from an appropriate material and exhibits an improved sensitivity and a greater resistance change than a sensor using the AMR effect. In this type of MR sensor, an in-plane resistance between a pair of ferromagnetic layers isolated by a non-magnetic layer changes in proportion to a cosine of an angle defined by the magnetization directions of the two layers.
Japanese Patent Publication (Unexamined) No. A-02-61572 associated with a priority date in June, 1988 [1] discloses a layered magnetic configuration that brings about a high MR change generated by anti-parallel arrangement of magnetization within magnetic layers. Document [1] describes ferromagnetic transition metals and alloys as materials that can be used for the layered configuration. Moreover, Document [1] discloses a configuration in which an antiferromagnetic layer is added to at least one of two ferromagnetic layers isolated by an intermediate layer and that the antiferromagnetic layer is preferably made from FeMn.
Japanese Patent Publication (Unexamined) No. A-04-358310 associated with a priority date of Dec. 11, 1990 [2] discloses an MR sensor having two ferromagnetic thin film layers isolated by a non-magnetic metal thin film layer, in which MR sensor when the magnetic field applied is 0, the two ferromagnetic thin film layers have magnetization directions vertically intersecting each other and the resistance between the two ferromagnetic layers not connected changes in proportion to a cosine of an angle defined by the magnetization directions of the two layers independently of a current flowing in the sensor.
Japanese Patent Publication (Unexamined) No. A-06-203340 associated with a priority date of Aug. 28, 1992 [3] discloses an MR sensor based on the aforementioned effect and having two ferromagnetic thin film layers isolated by a non-magnetic metal thin film layer, in which MR sensor when an external magnetic field applied is zero, magnetization of an antiferromagnetic layer adjacent to one of ferromagnetic layers is kept vertical to the other ferromagnetic layer.
Japanese Patent Publication (Unexamined) No. A-07-262529 filed on Mar. 24, 1994 [4] discloses a magneto-resistance effect element as a pin bulb having a layered configuration of a first magnetic layer, a non-magnetic layer, a second magnetic layer, and an antiferromagnetic layer, the first and second magnetic layers using CoZrNb, CoZrMo, FeSiAl, FeSi, or NiFe materials, which may also contain Cr, Mn, Pt, Ni, Cuy, Ag, Al, Ti, Fe, Co, and Zn.
Japanese Patent Publication (Unexamined) No. A-07-202292 filed on Dec. 27, 1993 [5] discloses a magneto-resistance effect film having a plurality of magnetic thin films layered via a non-magnetic layer on a substrate and an antiferromagnetic thin film provided adjacent to one of soft magnetic thin films separated by a non-magnetic thin film, wherein the antiferromagnetic thin film has a bias magnetic field of Hr greater than a coercive force Hc2 of the other soft magnetic thin film, and the antiferromagnetic film is made from at least one of, or a mixture of NiO, CoO, FeO, Fe.sub.2 O.sub.3, MnO, and Cr. Moreover, Japanese Patent Application No. 06-214837 filed on Sep. 8, 1994 [6] and Japanese Patent Publication (Unexamined) No. A-08-127864 filed on Nov. 2, 1994 [7] disclose a magneto-resistance effect film, wherein the aforementioned antiferromagnetic film is a superlattice made from at least two materials selected from a group consisting of NiO, NixCo1-xO, and CoO.
Furthermore, Japanese Patent Publication (Unexamined) No.A-08-204253 filed on Jan. 27, 1995 [8] discloses a magneto-resistance effect film characterized in that the aforementioned antiferromagnetic film is a superlattice made from at least two materials selected from a group consisting of NiO, NixCo1-xO (wherein x=0.1 to 0.9), and CoO, and that the atomic number ratio of Ni against Co in the superlattice is 1.0 or above. Moreover, Japanese Patent Application No. 07-136670 [9] discloses a magneto-resistance effect film characterized in that the aforementioned antiferromagentic film is a two-layered film made from 10 to 40 Angstrom of CoO formed on a NiO layer.
When actually mounting a magneto-resistance (hereinafter, referred to as MR) effect element on a recording/reproduction head, various thermal treatments are required after the MR effect element is formed, including a photo-resist hardening step for forming a recording head block. However, in a case of the spin bulb type MR effect element, magnetization of the antiferromagnetic layer is rotated by a thermal treatment and the spin bulb may not operate normally as an MR effect element. To cope with this, after forming a recording head block and a reproduction head block, the magnetization direction of the antiferromagnetic layer needs be corrected. However, if the temperature applied in this correction treatment is too high, the following two problems arise.
If a spin bulb type MR effect element is to have little hysteresis, i.e., little noise as a reproduction head in the magnetic field dependency characteristic, it is necessary to lower a coercive force of a free magnetic layer. For this, it is effective to maintain the magnetization axis direction of the free magnetic layer almost vertical against the magnetization direction of the antiferromagnetic layer. However, the direction of the magnetic field applied for correcting the magnetization of the antiferromagnetic layer is vertical to the axis of easy magnetization. Accordingly, if the treatment temperature is too high, the axis of easy magnetization of the free magnetic layer becomes almost parallel to the magnetization direction of antiferromagentic layer, deteriorating the noise characteristic of the reproduction head. Moreover, if the spin bulb is subjected to a thermal treatment of a high temperature, the non-magnetic layer may be dispersed into the magnetic layers, which in turn decreases the resistance change ratio, lowering the output of the reproduction head.
On the other hand, when using a material enabling to correct the magnetization of the antiferromagnetic layer at a lower temperature, the magnetization of the antiferromagnetic layer is rotated by an external magnetic field even with an operation environment temperature of a hard disc apparatus. That is, it becomes difficult to assure high reliability. From a viewpoint of an optimal spin bulb material design including a production procedure of the recording/reproduction head, it becomes important to be able to change the temperature at which the magnetization of the antifeerromagnetic layer is rotated, i.e., to be able to change a thermal treatment temperature for the aforementioned correction of the magnetization direction.